How to read a study

Before you read

It helps to know where the work was published and whether it went through peer review. Preprints, for example, are posted before that review. It is also worth checking who funded the study and whether the authors declare conflicts of interest.

What was studied and how

The methods section is the most important one. It shows whether the study was done in cells, animals or people; how many participants or samples there were; whether there was a comparison group; whether allocation was random and whether those measuring the outcomes knew which group each participant belonged to.

A weak design can produce striking results that are later not confirmed.

How to read the results

A “statistically significant” result means the observed difference is unlikely to be due to chance alone, but it does not say whether that difference is large or relevant. That is why it helps to look at the effect size and its confidence interval, not just the p value.

What was measured also matters: a change in a laboratory marker is not necessarily a change in people's health.

Limitations and replication

Good papers include a limitations section. Reading it helps you understand how far the conclusions go.

A single study is rarely definitive. Systematic reviews, which gather and appraise every study on the same question, usually give a more complete picture.

Useful questions

Before accepting a conclusion, you can ask:

• Was it studied in cells, animals or people?
• How many participants or samples were there, and was there a comparison group?
• What exactly was measured, and for how long?
• Is the effect large, or only statistically significant?
• Did other studies find the same?
• Who funded the work?